Please refer to FIG. 1, it shows the schematic circuit diagram of a conventional non-isolated boost DC/DC converter in the prior art. In which, the non-isolated boost DC/DC converter includes an input capacitor Ci, a main choke L, a switch Sm, a main diode Db, and an output capacitor Cb. The configuration of the boost DC/DC converter as shown in FIG. 1 is employed in the hard-switching module. If the switching frequency increases dramatically, the switching losses would also be increased dramatically, and the size of the heat-dissipating plate needs to be increased too. Besides, the EMI problem would become more serious due to the increased switching frequency, and the size of the EMI filter would be increased as well.
Please refer to FIG. 2, it shows the schematic circuit diagram of another boost DC/DC converter in the prior art, which is proposed to resolve the drawbacks of the above-mentioned conventional non-isolated boost DC/DC converter as shown in FIG. 1. In which, the boost DC/DC converter includes three diodes Dc, Da1, and Da2, a resonant inductor Lr, a transformer Tr, a resonant capacitor Cr, and a auxiliary switch Sa except for the original configuration of FIG. 1. Through the operations of these elements, the advantage of employing the soft-switching technique so as to have no switching losses can be achieved. This advantage of having no switching losses would make the increasing of the switching frequency become possible, and also has the effects of decreasing the EMI and the RFI. But, the configuration of the boost DC/DC converter as shown in FIG. 2 still has certain drawbacks such as the number of increased elements is relatively large, thus the size of the boost DC/DC converter can not be decreased in certain occasions. If the number of elements of the proposed boost DC/DC converter could be decreased further, it could be applied to an even broader range and would have an even better effect.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the applicant finally conceived the soft-switching DC/DC converter having relatively fewer elements. The proposed soft-switching DC/DC converter has the following advantages: decreasing the switching losses of the proposed converter, having relatively smaller sizes of the proposed converter (not only the main magnetic elements, but also the heat-dissipating plates, and all added elements for achieving the soft-switching are all downsized), decreasing the EMI of the proposed converter, increasing the efficiency of the proposed converter, and decreasing the total cost of the proposed converter relatively (for example, the sum of the manufacturing cost and the transportation cost is lower than that of the boost DC/DC converter of FIG. 2).